Liver & Pancreas Flashcards
How do pancreatic secretions travel to the duodenum?
Pancreatic duct –> common bile duct –> sphincter of Oddi
What percentage of the pancreas has an endocrine function?
1-2%
Which salivary gland does the exocrine pancreas resemble?
Parotid
How many enzymes are formed by the pancreas for digestion?
15
Where are the nuclei in pancreatic enzyme producing cells?
At the base
What is the structure of the exocrine glands in the pancreas and what type of secretion occurs here?
Branched acinar
Merocrine (into a central cavity)
What are centroacinar cells?
Cells that partially line lumen of acinus/duct
Secrete HCO3-
How can you tell the difference between acinar and centroacinar cells?
Nuclei are at the centre in centroacinar cells and at the base in acinar cells
What is different about the ducts of salivary glands and the exocrine pancreas?
No striated ducts in the pancreas
What do the islets of Langerhans look like?
Pale-staining, small with profuse blood supply
What is produced by the islets of Langerhans?
Insulin
Glucagon
Somatostatin
Vasoactive intestinal peptide VIP
Pancreatic polypeptide PP
How are the cells arranged in the islets of Langerhans?
Arranged in columns/cords around a capillary
Why are pancreatic enzymes secreted in proenzyme form?
Prevent self-digestion
What are the eight functions of the liver?
Exocrine - produce bile for duodenum
Process absorbed nutrients
Metabolism of carbohydrates, fats and protein
Involved in storage of carbohydrates, fats and vitamins
Synthesise and secrete plasma proteins and lipoproteins
Detoxification of ingested toxins, drugs
Destroys old RBCs and reclaims iron
First site of haematopoiesis in the embryo
How many lobules are in a human liver and what shape are they?
1 million
Hexagonal
Why are the lobules of the liver hard to distinguish in humans?
Less connective tissue between
How does the processed blood of a lobule enter the hepatic vein?
Sinusoids deliver to the central vein (of that lobule)
What are portal tracts?
Triad at vertices of liver lobules
Consist of a branch of:
- Hepatic portal vein (largest)
- Hepatic artery
- Bile duct
What does the hepatic portal vein do?
Delivers blood containing nutrients from small intestine to the liver
What does the hepatic artery do?
Delivers oxygenated blood to the hepatocytes/liver
What does the bile duct do?
Collects bile produced by hepatocytes
Which way does blood and bile flow in a lobule?
Blood = towards central vein
Bile = away from central vein
How are the hepatocytes arranged in the lobules and what do they look like?
Rows with sinusoids between; 1-2 layers of cells
Roughly cuboidal with microvilli
Describe the sinusoids of the liver.
Discontinuous and fenestrated endothelial cell lining
2-3 RBC diameter
Contain Kupffer cells
What is the function of the Kupffer cells?
Phagocytic - take up pathogens and particulate material
Where is the space of Disse?
Between endothelial cell lining of sinusoids and surface/microvilli of hepatocytes
What are the alternative names for Ito cells?
Hepatic stellate cells
Perisinusoidal cells
What is the function of Ito cells?
Store vitamin A in lipid droplets
Where are Ito cells found?
Space of Disse
How can Ito cells cause liver cirrhosis?
Inflammatory stimuli (eg. alcohol) can cause Ito cells to transform into myofibroblasts
Produce large amounts of collagen and ECM
Blocks blood/nutrient flow across lobule
Hepatocyte death
Why is it beneficial to have a discontinuous endothelial cell lining in the liver sinusoids?
Direct contact of blood with hepatocyte microvilli increases efficiency of transfer
How is bile delivered to the bile duct from the hepatocytes?
Bile canaliculi –> bile duct branch of portal tract –> Bile duct
Where are bile canaliculi found?
Between hepatocytes
What do hepatocytes secrete?
Albumin
Fibrinogen
Clotting factors
What prevents bile from moving between hepatocytes?
Tight junctions
What does bile contain?
Bile salts
Bile pigments
What are deoxycholate, sodium glycocholate and taurocholate examples of?
Bile salts
What are bile salts and what is their function?
Breakdown products of cholesterol
Detergents to emulsify fats in duodenum
What are the two bile pigments and what colours are they?
Biliruben - red
Biliverdin - green
What are bile pigments?
Breakdown products of haemoglobin
What is a liver acinus?
Body of tissue supplied by two triads
Which zone is the most oxygen-rich in a liver acinus?
Zone 1
What zone of a liver acinus would be affected first by phosphorus and why?
Zone 1
Immediately toxic to hepatocytes
What zone of a liver acinus would be affected first by paracetamol and why?
Zone 3
Toxic breakdown products
Describe how paracetamol is metabolised by the liver.
P450 used to convert paracetamol to a reactive quinone derivative
Reactive quinone derivative removed by glutathione
What substance is used to replenish glutathione levels?
Methionine
Why is an overdose of paracetamol so dangerous?
Glutathione supply depleted so reactive quinone derivative binds covalently to cellular proteins and kills cells
Liver failure
Why should you not ingest barbiturates and alcohol with paracetamol?
They induce liver enzymes which potentiates the toxicity of paracetamol
How much bile is stored in the gall bladder usually?
50ml
How does the gall bladder concentrate bile?
Na/K-ATPase pump on BL membrane pumps Na+ across membrane (absorbed)
Water follows by osmosis
What type of epithelium lines the gall bladder?
Tall, simple, columnar epithelium with irregular brush border
Why does it look like there are cracks between the basal surfaces of adjacent cells lining the gall bladder?
Influx of water following NaCl pumping into interstitial space
What stimulates the smooth muscle of the gall bladder to contract?
Cholecystokinin
Where is cholecystokinin produced?
Cells in base of crypts of duodenum
